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250 ox66 long block swap starts but won't stay running

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  • #1

    250 ox66 long block swap starts but won't stay running

    I just bought a boat with twin 1999 model 250 ox66 outboards. One motor was blown but the deal came with two new long blocks. I swapped the new long block on the bad motor and during the swap cleaned everything and changed the high pressure pump and filter, and the primary filter in the bowl right at the fuel connection. I was running 25:1 pre-mix to it from a separate can while I confirm the oil injection is working properly, and it calls for double oil during breakin. I bulb primed it and cracked open the drain on the VST to verify fuel had made it that far and the check valve wasn't clogged. I turned the key to run and the high pressure pump came on for ~ 4-5 seconds and I purged some fuel out the schrader to make sure the rail was full. Cycled the key again to re-pressureize the rail and then started it. It fired up quickly revved to 900 rpm then stuttered its way back to 0 rpm with in 2 seconds. I hit the starter again and its sputtered enough to disengage the starter but that was it. Cycling the key to off then on again will get it to run for a couple seconds again but thats it. I'm getting pressure at the schrader valve even after it shuts off. I'll take the pressure regulator off tonight and clean it, but any other suggestions are greatly appreciated. I will say that the long block swap was very simple and only took about 10 hours to do.

    Thanks in advance
    Dave
    Tags: None
  • #2
    Run with pressure gauge on schrader

    Comment

    • #3
      I hooked up the gauge to the port motor (the one thats still all original) and it had 30 psi while running. I hooked the gauge to the stbd motor with the new long block on it and turned the key to run. The pump came on and the gauge showed 30 psi. I start the engine and try to make it back there before it quits to read the gauge. After doing this a few times and not making it, it started running longer until it just didn't quit. So now it runs and the gauge shows 30 psi while running. Not sure why it didn't stay running on the first few tries, but about 20 start cycles later it runs nice and smooth.

      I know some car ecu's, computers, control module things take a little while to "learn" the sensors again after they've been sitting and I think this one has been sitting for 2 years or so... maybe that's it???

      Now I have to check the oil injection flow on both motors, change the filters on the port motor, rebuild all 6 trim cylinders, figure out how much fuel I have in the tank and add the right amount of oil, fix the start / kill switches on the tower, bleed the air out of my new seastar rams and both helm pumps... then I can go break in the new block for 10 hours

      Great forum, I'll be back I'm sure.

      Dave

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      • #4
        there is NO learning curve on the ECU.
        did you carefully test the O2 sensor output?
        your describing bleeding the air out of the fuel rail.

        did you test/check the injectors?

        a blown powerhead is a symptom of a problem, NOT the problem.

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        • #5
          I did not test the injectors, and it didn't run long enough to test the O2 sensor. I can test the O2 now that it runs. What should the O2 voltage be while idling? How do I test the injectors?

          The original block developed a 1/2" hole in the side of the block at a water jacket that was obviously blowing gallons of seawater under the cowl. The previous owner discovered this while he was flushing it out after a day of fishing. He drilled and tapped it for a 1/2" pipe plug and hoped for the best. A few months later it locked up on him while running out maybe 20 minutes after he left the dock. It fired up for him again when he got back at the dock, but he ordered two new blocks and never got around to doing the swap. I'm assuming the seawater / vapor from the water hitting the cowl caused excessive corrosion and he didn't use the boat enough to keep the pitting down and the bearings just got so bad that it seized, but I would like to verify everything else is functioning ok before I take it out.

          Now that its running on 25:1 mix from a can I plan on checking the oil injection pump flow rate, but what else should I check?

          Thanks
          Dave

          Comment

          • #6
            I did some reseatch, and pulled the injectors out yesterday, and am going to send them to brucato today. Any thoughts on this? Seems like a scam to me sort of like paying some quick lube outfit to clean your spark plugs... i guess for $150 its pretty cheap to get them tested and cleaned.

            On the O2 sensor test. My manual says to torch it with mapgas and measure the voltage differential... really??? There has to be a more refined method to prove out these motors. When testing the knock sensor it says to smack it and test for voltage or resistance changes???

            Whats this test harness i read about. I see them on andys test equipment site, which one do i need and what can i test with it?

            I guess im used to working on newer common rail diesel marine engines using laptops and maybe more refined methods, but im all about simple is better, i just need some pointers to get me started.

            Thanks for the help so far i sure dont want to roast another block so let me know what else to test.

            Dave

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            • #7
              anyone have any input on which test harness to buy for my 99 model 250 ox66's? Anyone have any links on how to use said harness?

              Thanks
              Dave

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              • #8
                flame test is a teat on a boar hog for the O2 sensor.
                there are some tech bullitens that are much better.
                but if it wont stay running you have other issues.

                its just like a car motor, right?

                Comment

                • #9
                  Originally posted by rodbolt17 View Post
                  flame test is a teat on a boar hog for the O2 sensor.
                  there are some tech bullitens that are much better.
                  but if it wont stay running you have other issues.

                  its just like a car motor, right?
                  Right. I got both running fine, but before i go for a 10 hour breakin run i want to go through everything on the motors, hence i would like to know which harness(s) i should buy and how to use them. I found a bulletin on testing the O2 while its running and read some more post about it so im good there but what about the rest of the sensors?

                  Also how do you know the oil injection pump is working? Sure there are alarms for oil level, but if a hose cracks or the pump quits the only alarm you get is a screaching sound right before total silence??? Anyone ever put a flow meter or pressure gauge on the system?

                  Comment

                  • #10
                    I received my stbd injectors back from Brucato who said two where rich at idle and two others where rich off idle and up. So I'll put those back in and probably send the port motor's stick out to them as well. They where very professional and curtious, and its good knowing my injectors are good as new.

                    I ordered all the o-rings for the tilt/trim cylinder since all mine are leaking, new oil tank filters both remote and on engine filters and the gasket thing for the on engine tank filters, all 6 low pressure pumps, the tilt trim tool and the O2 sensor test harness, along with gear case oil and o-rings, and trim/tilt fluid all from Andy at SIMYAMAHA.com. I still have to put on the new fuel filters for the port engine, check and adjust the oil injection pump, figure how much fuel is in the tank and add the appropriate amount of oil to the tank then I'll go out for the break-in run on the new long block. I may talk myself into swapping the other new long block on the port motor so I only have to do the break-in thing once... I could do it in a weekend but that's one more weekend I'm not boating

                    Andy has been great by the way, quickly replying to my e-mails searching for those hard to find o-rings and such. Even with some "connections" in the boat business I still can't find better prices on the stuff than what Andy has. Guess I found my parts guy...

                    Dave

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                    • #11
                      did you check for parts on this site?

                      How old is the fuel in the tank and is it ethanol free?
                      old fuel is not good for motors


                      Manual should give procedure for measuring oil out put over a set time, and cleaning/ flushing checking check valves and oil lines

                      Comment

                      • #12
                        Originally posted by 99yam40 View Post
                        did you check for parts on this site?

                        How old is the fuel in the tank and is it ethanol free?
                        old fuel is not good for motors


                        Manual should give procedure for measuring oil out put over a set time, and cleaning/ flushing checking check valves and oil lines
                        The fuel in the tank is probably 18 months old. Non ethanol. The gauge registers about half a tank which would be 135 gallons. Since i have a 10 hour breakin schedule to make i figured i would burn through a full tank so ill dilute the old non ethanol fuel with fresh non ethanol and add the oil then burn it all during breakin.
                        I changed all the filters in the boat and will change all the filters on the motors before the run, and all the oil filters and test the oil injection system as well. Trying to be thorough although i admit im a rookie with these small gas engines so i appeeciate all the advice i can get.

                        Thanks
                        Dave

                        Comment

                        • #13
                          If you put 135 gallons of fresh gas in 135 gallons of bad gas you end up with 270 gallons of bad gas,
                          Just my opinion

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                          • #14
                            I'll second the opinion.

                            Comment

                            • #15
                              Originally posted by 99yam40 View Post
                              If you put 135 gallons of fresh gas in 135 gallons of bad gas you end up with 270 gallons of bad gas,
                              Just my opinion
                              Really? If i burn it all over two weekends and then refill with fresh fuel i would think its fine. The problem with old fuel is it sits and gunks up everything right? So if its flowing through and not sitting it should be fine as long as the octane is high enough to keep it from detonating. I dont have a good way to get rid of that much fuel anyway. Maybe im ignorant to other effects of old fuel, ill get rid of it of i have to but please advise with bad fuel effects so i can make a more educated decision.

                              Thanks
                              Dave

                              Comment

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